1. Field of the Invention
This invention relates to a semiconductor laser, and more particularly to compositions of semiconductor layers of a semiconductor laser.
2. Description of the Related Art
As semiconductor lasers emitting a laser beam of 0.7 to 0.85 .mu.m, there have been wide known those comprising an n-AlGaAs clad layer, an n- or i-AlGaAs optical waveguide layer, an i-AlGaAs active layer, a p- or i-AlGaAs optical waveguide layer, a p-AlGaAs clad layer and a p-GaAs capping layer formed on an n-GaAs substrate in this order. See, for instance, "Appl. Phys. Lett., 39(1981)134".
However this structure is disadvantageous in view of reliability in that since Al contained in the active layer is chemically active and is apt to be oxidized, the end face of the resonator formed by cleavage is apt to deteriorate.
Thus there has been proposed as described in "Jpn.
J. Appl. Phys., 31(1992)L1686" a semiconductor laser comprising an n-InGaP clad layer, an n- or i-InGaAsP optical waveguide layer, an i-InGaAsP active layer, a p- or i-InGaAsP waveguide layer, a p-InGaP clad layer and a-GaAs capping layer formed on an n-GaAs substrate.
However this structure is disadvantageous in that diffusion of In takes place in the course of growth of the structure, which makes unstable the state of the crystal faces, and accordingly it is impossible to generate interfaces on opposite sides of the active layer at a high quality with a stable reproducibility.
Further as semiconductor lasers emitting a laser beam of 0.98 .mu.m, there has been proposed as described, for instance, in "Appl. Phys. Lett., 62(1993)1644" those comprising an n-InGaP clad layer, an n- or i-InGaAsP optical waveguide layer, an i-GaAsP tensile strain barrier layer, an i-InGaAs compression strain active layer, an i-GaAsP tensile strain barrier layer, a p- or i-InGaAsP optical waveguide layer, a p-InGaP clad layer and a p-GaAs capping layer formed on an n-GaAs substrate.
However this structure is disadvantageous in the following points. That is, in crystal growth by MOCVD (metal organic chemical vapor deposition) method, a rapid substitution of As on P takes place upon switching of hydrogenated V group gases (PH.sub.3, AsH.sub.3) in the course of growth of the clad layer/optical waveguide layer interfaces and the barrier layer/active layer interfaces or growth reverse thereto, which makes unstable the state of the crystal faces. Accordingly it is impossible to generate the interfaces at a high quality with a stable reproducibility and the quality of crystals grown on the interfaces deteriorates.